1. Field of the Invention
The present invention relates to a seat structure, to be more in detail, relates to a seat structure suitable used for a seat for a transportation machine such as a plane, train, ship, fork lift, and automobile, or for various chairs or wheel chairs used in the inside or outside of a building.
2. Description of the Related Art
For a seat for a plane, train, ship, automobile, and the like, not only improvement of basic functions such as impact absorbency, vibration absorbency, and so on, but also to supplement these functions and obtain better ride comfort, improvement of various functions such as physique difference absorbency, posture difference absorbency, body movability, and so on are always requested. Further, in recent years, in order to reduce weight of transportation devices such as automobiles from the view point of environmental measure by improving fuel economy, in addition to improvement of various functions described-above, the reduction in weight of seat used for these transportation devices is required, and technology to use a thinner and lighter cushion material and the like are proposed.
For instance, from the above point of view, the present applicant has proposed a seat structure with sufficient characteristics (spring characteristic and damping characteristic) as a cushion structure though light in weight by using a three-dimensional net member (a solid knitted fabric) having a thickness of about several millimeters to several tens millimeters strained to frames as a tension structure.
However, in order to display sufficiently the characteristics required for a seat of automobile or the like using such a solid knitted fabric, it is necessary to make vibration absorbency, physique difference absorbency, and the like serve effectively by disposing a flat-type supporting member composed of a two-dimensional net member or a solid knitted fabric, or a flat-type elastic member called Plumaflex under the solid knitted fabric, and by supporting it with plural metal springs (coil spring) to supplement a feeling of spring and to support the load dispersedly. However, when plural coil springs are disposed, since the solid knitted fabric itself is thin, a seated person often feels hitting of the coil spring under the solid knitted fabric as a feeling of something foreign. Accordingly, increase of number of solid knitted fabric layers or disposition of other cushion structure such as a urethane member between the solid knitted fabric and the coil springs have been put into practice conventionally. Therefore, if the number of disposed coil springs that cause a feeling of something foreign can be reduced, or if the coil springs can be disposed to somewhere not likely to be felt as a something foreign, further reduction in weight can be expected by reducing the number of the solid knitted fabric layers or disappearing of necessity to intercalate other cushion structure such as a urethane member.
When the urethane member that has been generally used as a cushion structure is used, in order not to make a seated person feel something foreign for items different in stiffness such as wire and frames, it is a usual manner to ensure the thickness of urethane to be 30 mm or more. But when material that is made thinner in thickness and lighter in weight is used, there arises a similar disadvantage as the case of the solid knitted fabric. When other cushion structure such as a two-dimensional net member containing an elastic yarn is used, there arises a similar disadvantage due to thinness of the thickness. When plural two-dimensional net members, solid knitted fabrics, or urethane materials are used in combination in arbitrary number, a thinner and a lighter cushioning structure can be obtained by reducing the number of disposing the coil springs or changing the place of disposition.
Further, in particular, as for the impact absorbency required for a seat for transportation device such as an automobile, reduction of rebound of the human body from a seat at the time of collision is required. As a measure for this requirement, required is a structure to disperse a collision load received in the longitudinal direction by changing a seating angle so that depression of the haunches becomes large through conversion of the rotational moment of inertia force around a tuber of ischium.
On the other hand, a standard posture of a person seating on a chair is a state that the haunches are positioned at the rear of a seat cushion of the chair, and the waist abuts on a seat back of the chair. However, it is reported that, as a seating posture of a person, especially in the case of a small physique such as an elderly person and a child, or in the case of seating for a long time, a way of sitting called a sacrum posture that the haunches move toward front to make the sacrum portion touch a seat cushion (Study of Designing Bulletin of JSSD Vol. 48, No. 1, 2000. p49 to 56, “Suspension Optimum Characteristic of a Wheel Chair for Handicapped Person Taking Difference in Physique into Consideration”) The same thing can be said of a seat for a transportation device such as an automobile, a chair for office work or for theater as well as a wheel chair, and required is development of a seat structure which absorbs difference in physique and difference in posture without damaging impact absorbency or vibration absorbency so much and attains a comfortable feeling of seating.